Astronomy and Astro-Physics Volume 12

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1893 Excerpt: ...three times the diameter. Saturn's ring is ten thousand miles in breadth. Its thickness is unknown, but it has been variously estimated at from forty to one hundred and forty miles. As any satellite composed of particles free to move among themselves revolves about its primary, there will be a tendenc' to form tides within it elongating the satellites in the direction of the radius vector. Owing to the rotation of the satellite, the elongation will really make a certain angle with this line. The attraction of the primary acting upon these protuberant regions tends to give the satellite a rotation, the same in direction and period as that of its revolution in its orbit. But a satellite revolving in a retrograde direction is under these circumstances in a position of unstable equilibrium, and the slightest disturbance of its plane of rotation will cause it under this tidal retardation to change its plane with increasing velocity, until it is placed at right angles to the plane of its orbit. After that the change will continue with diminishing intensity until a direct rotation is established coincident with the plane of the orbit. It will be noted that this disturbing force acts at right angles to that producing the precession of the equinoxes. Those who desire a visible illustration of this change of plane can readily obtain it with an ordinary gyroscope. If through condensation, the tides cease before this result is attained, the satellite will continue to rotate in a plane more or less inclined to that of its orbit. The periodically flattened appearance of Jupiter's outer satellites, however, is not due to the tides, which although theoretical some miles in height, could not be seen from the Earth. What applies to the larger planets is upon this theory true...